1. Field of the Invention
The present invention is directed to an apparatus for treating a subject with focused ultrasound waves, of the type having an ultrasound transducer composed of a plurality of ultrasound transducer elements and having a means for driving the ultrasound transducer that supplies electrical signals to the ultrasound transducer elements of the ultrasound transducer offset relative to one another in time corresponding to a desired position of the focus.
2. Description of the Prior Art
An apparatus of the above type is employed, for example, for treating pathological tissue changes. The pathological tissue is thereby heated by focused ultrasound waves emitted as therapeutic acoustic waves. Insofar as the occurring temperatures lie below 45.degree. C., the metabolism is disturbed, with the result that, in the case of tumors, a retardation of the growth or even a regression of the tumor occurs. This type of treatment is known as local hyperthermia. When temperatures beyond 45.degree. C. are reached, the cell protein coagulates, resulting in the necrotization of the tissue. This latter type of treatment is called thermotherapy.
The therapeutic acoustic waves are emitted as continuous sound or pulsed continuous sound.
A therapy apparatus of the type initially described can also be employed in the treatment of stone conditions (lithotripsy) and bone conditions (osteorestoration). The therapeutic acoustic waves are then emitted in the form of shock waves.
The possibility of being able to displace the focus of the acoustic waves is provided in order to enable a displacement of the focus within the subject to be treated without the ultrasound transducer and the subject under treatment having to be shifted relative to one another.
An apparatus of the type initially described is disclosed, for example, in German OS 43 02 538 . In this apparatus, the displaceability of the focus is realized in that a delay element with adjustable delay time is allocated to each of the ultrasound transducer elements. The delay elements serve the purpose of delaying the signals supplied to the ultrasound transducer elements from a single oscillator for ultrasound generation or changing their phase position such that a desired focus position derives. The delay times of the delay elements are set with a control unit. Rather substantial technical outlay must thus be employed involving correspondingly high costs. Moreover, the complicated structure of the electronics involves a high space requirement.
Whereas a common oscillator supplies the signals required for ultrasound generation for all ultrasound transducer elements in the case of German OS 43 02 538, a drive circuit is allocated to each ultrasound transducer element in the case of an apparatus disclosed by U.S. Pat. No. 5,065,741, this drive circuit supplying the signals required for ultrasound generation to the respective ultrasound transducer element, whereby the points in time of the activation of the drive circuits are set by a computer--to which a memory is allocated--dependent on the interpretation of ultrasound images generated with an ultrasound locating means.
U.S. Pat. No. 5,158,071 also discloses an apparatus wherein a drive circuit is allocated to each ultrasound transducer element, this drive circuit supplying the signals for the respective ultrasound transducer element required for ultrasound generation, whereby the points in time of the activation of the drive circuits is set dependent on the respectively desired position of the focus.
German OS 30 48 527 discloses a diagnostic ultrasound applicator wherein a shared oscillator supplies the signals required for ultrasound generation for several groups of ultrasound transducer elements. The signals of the oscillator are thereby supplied to the individual groups via corresponding drive switches that are activated with a digital control element, for example an 8-bit D-register.
German OS 32 36 218 discloses a diagnostic ultrasound applicator wherein a demultiplexer/transmission unit supplies the signals required for the ultrasound generation for the ultrasound transducer elements. These signals are thereby supplied to the ultrasound transducer elements dependent on delay times stored in a memory.